Our lab explores the question of how and where hormones act in the central nervous system to alter parental behavior and physiological adaptations associated with parenting. Because of its strong functional association with parental care in a wide range of vertebrate species, we are particularly interested in the pituitary hormone prolactin. To explore the mechanisms by which prolactin promotes parental responsiveness, we have chosen the ring dove as a model system. Ring doves are attractive animals to study in this context because they exhibit an unusually rich repertoire of behavioral responses relating to parental care that have already been shown to depend on prolactin for their expression. This repertoire is displayed by both parents and includes nest defense, incubation of eggs, brooding of young, regurgitation feeding of young, and increased parental foraging to support nestling growth. As in mammals, prolactin also stimulates the growth of a “milk” producing organ (the crop sac) for provisioning the young and strongly inhibits gonadal activity during the parental phase of the ring dove breeding cycle. Because reproductive suppression also occurs naturally in lactating women nursing young and in women suffering from chronic elevation in plasma prolactin levels (hyperprolactinemia) due to pituitary tumors, investigations using this model system may shed light on the etiology of a common cause of clinical infertility and the physiological mechanisms underlying lactational amenorrhea (cessation of menstrual cycles).

Activation of neurons in the interpeduncular region of the dove midbrain during incubation as revealed by increased Fos protein expression.

My lab has adopted a variety of experimental approaches to uncover the neural and hormonal mechanisms responsible for parental behavior expression and physiological adaptations associated with care of young. Autoradiographic techniques have been used to map the location of prolactin receptors in the dove central nervous system. Areas of high receptor density have been further explored as potential sites of prolactin action in altering specific behavior patterns and changes in neuroendocrine function using microinjection and lesioning techniques. We have also used immunocytochemistry for immediate-early gene products to identify brain areas that are activated in response to prolactin stimulation and changes in the social and physical environment. Most recently, we have cloned several genes that change in response to prolactin stimulation and code for proteins that play an important role in the parental effort. Currently, we are measuring the expression of these genes in dove brain by in situ hybridization and quantitative RT-PCR. We have also developed methods to examine changes in the signaling pathways that prolactin uses in its target cells, which provides us with an opportunity to explore how these signaling pathways are altered in response to hormonal and environmental changes during parent-young interactions and by previous experience in raising young.

Prolactin-induced increases in cells expressing the appetite stimulant, agouti-related peptide, are seen during the post-hatching period when parents increase their foraging activity to feed their young.

One of the most exciting findings of recent years is that avian and mammalian brains also produce their own prolactin-like molecules, which raises questions about the relative importance of pituitary prolactin and "brain prolactin" in regulating behavioral changes and changes in patterns of hormone secretion. By adopting a comparative approach to address this question and related questions of prolactin physiology, we hope to make an important contribution to the formulation of general principles that govern neural and hormonal regulation of parental care.